The broad objective of the proposed research is the synthesis, characterization and study of the reactivity of a broad class of metal complexes of iron and cobalt (and their congeners ruthenium and rhodium) which may serve as models for their naturally occurring biological counterparts. The proposed ligand systems are being designed to contain a variety of electronic and structural features, in particular steric constraints; that will encompass those of naturally occurring heme and corrinoid systems. Three areas are being focused upon: 1) the interaction of oxygen and carbon monoxide with iron (II) and ruthenium (II) complexes, 2) new cobalt (III)-alkyl complexes containing strained Co-C bonds and 3) the synthesis characterization and study of co-facial binuclear metal complexes in which the metal atoms are intentionally positioned such that both metals must interact with substrates positioned between them. The electronic and molecular structures of all new complexes will be examined with electronic and nuclear mangetic resonance spectroscopy and selected compounds will be subjected to full scale structural determination via X-ray crystallography.